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Sound Devices MixPre-D – is it working properly?
Just snagged one of these from ebay. This is my first piece of pro audio gear. I do videography work, mostly live events, and I needed a decent pre-amp since the pre-amps in my Tascam DR-100 weren’t quite cutting it.
I notice when I have the headphone level set to 0db and have no mic connected or a mic connected and not set to phantom power (my mic needs phantom power) I start to hear a little noise/hiss with the gain pot set to 11 o-clock and hear noticeable noise/hiss from 1 o-clock to max gain.
I also notice with a quick recording into Adobe audition via the USB interface, I get the same result – slight bit of noise/hiss in the recording past 60% gain with no mic attached.
Doesn’t sound like interference, just like I hit the noise floor. I suspect that a unit with this much gain simply is supposed to work this way, but I wanted to see if you had any experience in sound and could just confirm. It’s possible that there’s no such thing as a pre-amp with zero noise with the gain set to 60% or higher, but again, I’m new to this, so I simply don’t have any point of reference.
Can anyone confirm that this is normal operation for this device, or should I get it serviced?
Thanks so much!
Jonathan
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17 Replies
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[Jonathan Hardison] “Can anyone confirm that this is normal operation for this device, or should I get it serviced?”
It’s not normal to “use” the unit without a mic, no. Try using a mic before you decide it’s defective.
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I get the same noise with or without a mic. I’m trying to set a baseline.
Say, for instance, is there any such thing as a pre-amp that has no noise/hiss at all when set to 100% gain?
Thanks!
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[Jonathan Hardison] “I get the same noise with or without a mic.”
Really? Because there’s a world of difference between an open circuit and a low impedance microphone. A microphone is low impedance so that real physical current flows in the wires going to the mic. The micpre the microphone is connected to typically has a higher impedance so that this current can develop sufficient voltage that the micpre has something to amplify. Without this voltage across the input to the micpre, the micpre is operating outside its design specifications. Said another way, without an input voltage, the output of the micpre is largely undefined.
I’m just saying that you can’t meaningfully “set a baseline” for a micpre using an open circuit.
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That’s good to know. Makes sense.
I guess a better worded version of my question is:
Can anyone who has experience with a MixPre-d, a Sennheiser ME66/K6 shotgun and Sony 7506 headphones confirm if you get any noise while phantom powering the mic, setting the headphone level to 0db and cranking the gain to 100% in a quiet room? Do you get that same noise at 100% gain from a recording with the unit plugged into a computer via USB?
I may be naive in expecting a pre-amp to have no noise at higher gain levels using the microphone that I’m using, but I have no frame of reference, which is why I’m asking.
Thanks again!
Jonathan
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One thing you need to understand is that most level control circuits are logarithmic, not linear.
As the control gets toward the top of the scale, (or the bottom for that matter) the boost or cut is increased much more rapidly than on a strict 1 to 1 basis.
Look at the db readings and you’ll see that at the extremes, theres typically a LOT more cut or boost than there is near the zero position. Which could mean that at the 100% boost position, you’re getting a LOT of gain added to accommodate the HUGE difference between, for example, the amplitude of a line level signal and a mic level signal. Those two things are VERY different. So a fader designed to handle both, needs a BIG range of boost and cut over it’s travel.
So “turning it up to 100” is often NOT a particularly sensible way to operate a mixer.
Obviously, all this depends on how the particular circuits are designed. But just because the fader travels 6 inches that doesn’t mean that the first inch is simply six times quieter than the 6th inch. It typically doesn’t work that way.
FWIW.
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I’m simply trying to figure out if my mixer is operating properly, or if there is an undue amount of noise.
Is there a way to do that?
Thanks!
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i have one, I’ll check later this AM. I don’t believe this is normal behavior. Just used mine Sunday and did not hear hiss at all.
Al
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I just checked it out. No. At 11 O’clock position, there is no noise floor at all. First off, check your batteries to make sure they are good. I always put a meter on them and they should be above 1.3V. Below that I often notice noise on various devices, like mics that use batteries instead of phantom. If you use fresh batteries and are still getting a noise floor at 11 with a mic attached, contact Sound Devices and have them service it.
Al
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Thanks a ton, Al. That’s really helpful. Could you verify that you had your headphones at 0 db? I don’t hear any hiss at 11:00 with the headphone output at -12db.
Thanks again!
Jonathan
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No. I hear no hiss when I plug in my headphones, dial in 0 dB for them, and have my gain control for the mic at 11:00. I’m using batteries on both the unit and the mic ( an AT897) that read at or over 1.35V. There’s a sound floor that shows up close to +20 but it should.
Al
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